Maria Kunz, a barmaid and hostess, is found strangled in her apartment on Helvetiastrasse. Gaudenz Moser is seen at the scene of the crime as he drives away on his motorcycle. He has an accident and is arrested. All the evidence points to him. His brother Vinzenz Moser calls on Iseli, the pastor of his home parish in Graubünden, for help. Iseli immediately sets off for Zurich, where the case has already been closed by the police because a confession has been made. Pastor Iseli, who has a keen sense of criminal investigation, does not believe that Gaudenz Moser is guilty and begins his own investigation in Zurich's underworld.